Various ambulatory medical devices have been proposed and a number of such devices are commercially available. These devices include implantable infusion pumps, externally carried infusion pumps, implantable pacemakers, implantable defibrillators, implantable neural stimulators, implantable physiological sensors, externally carried physiologic sensors, and the like.
Implantable infusion pumps are generally configured to accept infusion commands from an external communication device via an RF telemetry system, or the like. These commands are, inter alia, used to set program variables that are in turn used in defining the quantity and/or timing that is used in supplying a drug to the patient. As the dispensing of appropriate amounts of the drug may be critical to the patient's well being, it is important that a reliable communication channel exist between the external communication device and the implantable device.
Implantable devices typically operate by battery power. The batteries may or may not be rechargeable. Higher consumption of power from an implantable device containing non-rechargeable batteries leads to a shortening of the usable life of implantable device and an associated increased frequency of surgery, potential pain, recovery, and inconvenience. Higher consumption of power from an implantable device containing rechargeable batteries leads to more frequent charging periods for the batteries and associated inconvenience and may lead to an overall shortening of the usable life of the implantable device. As such, whether or not an implantable device contains rechargeable batteries or non-rechargeable batteries, it is desirable to lower the power consumption of device. As telemetry reception and transmission are highly energy consumptive, it is desirable to minimize the operation time of telemetry reception and transmission modules. As such it is desirable to ensure that message length is kept to a minimum and that repeated transmissions and attempted receptions of previously sent but unsuccessfully received messages be kept to a minimum.
As such, a need exists in the field for improved reliability of message reception. More particularly, a need exists in the art for improved information transfer efficiency by the communication system while holding the time period that the communication system is powered to a minimum. Furthermore a need exists in the art to minimize the number of communication attempts that must occur to successfully complete transfer of a message.
Some digital communication receiving systems and methods depend on the regular receipt of bit transitions in order to maintain bit synchronization between the transmitter and the receiver. This dependency is not generally a problem when messages are short but can become problematic when message length increases as the message may contain extended portions where few or no bit transitions occur. The maximum message segment length for which synchronization can be retained without bit transitions occurring depends on the type of communication system being used and the difference in clocking frequency between the transmitter and receiver.
As such, a need exists in the field for an improved way of ensuring maintenance of bit synchronization between receiver and transmitter particularly while not increasing, or at least not significantly increasing, the length of a message that is necessary to convey a given quantity of information.